Radiator balancing and pump speed

[JonathanM]

I want to try to balance my radiators for the first time, to try to get the lounge to heat up more quickly. The lounge is the last radiator in the downstairs zone. At the moment the lockshields are all fully open.

I've been reading through some previous threads, but there's a couple of basics I can't get my head around. Does closing the lockshields down mean there is more resistance in the system? or less resistance? Will I need to increase the pump speed or reduce it?

 

[JonathanM]

My pump is a BG Multihead G, made by Grundfos. I've seen at least two different versions of this. Mine has 3 speeds, 40W, 65W and 95W.

I think it is the same as this version of Grunfdos UPS 15-60. Everything looks the same. There seems to be a huge difference between settings 2 and 3 so I'm worried about it being too powerful on 3. To date it's always been on 2.

 

[denso13]

To date it's always been on 2.

Just try it and see. Balancing is normally straightforward, try not to overthink it.

 

[Johntheo5]

If you have a sealed system then speed 3 might be the better choice if you have > 10/12 rads, if a OV system then that speed/head of up to 5.8M may cause air ingress through the vent so speed 2. Basically you throttle in one valve on each rad (lockshield valve) you should throttle the rads nearest the boiler/pump first, best way IMO is to fully shut the lockshield and then open it say a 1/4 to 1/2 turn, most lockshield valves will give full flow with little or no (required) restriction even when opened only 1 full turn.

Balancing Heating Systems: Ensure Even Radiator Heat

The Ultimate Guide to balancing heating systems. Balancing a heating system is simply making sure all the radiators or emitters heat up evenly.

www.heatgeek.com

 

[JonathanM]

If you have a sealed system then speed 3 might be the better choice if you have > 10/12 rads, if a OV system then that speed/head of up to M may cause air ingress through the vent so speed 2. Basically you throttle in one valve on each rad (lockshield valve) you should throttle the rads nearest the boiler/pump first, best way IMO is to fully shut the lockshield and then open it say a 1/4 to 1/2 turn, most lockshield valves will give full flow with little or no (required) restriction even when opened only 1 full turn.

Thanks, that sounds very sensible. I've finally got my IR thermometer to give realistic readings, so will give it a go.

It's a 16 radiator open vent system, mainly double convectors.

 

[Johntheo5]

Those pump curves certainly don't help IF your system tends to pull in air at high heads.
A circ rate of 1LPM/kw will give a dT of 15C (rads) so 16 rads averaging 1.5kw/rad = circ flow of 24LPM or say 1.5ms/hr, speed 2 will only circulate this at a very low head of 1.0M, not a hope IMO of balancing anything at that very low head, spped 3 will circulate 1.5m3/hr at a head of 4M, perfect for balancing but possibly not for a OV system. Maybe before attempting balancing at speed 2, c/o to speed 3 and see if any pump over or air ingress, get someone to start/stop the boiler/pump (speed 3) while you watch for any spurts of water from the vent when the boiler is both sarted and stopped.

 

[JonathanM]

I hardly ever use upstairs these days, so rarely turn that zone on.

There are eight radiators downstairs. Could I just balance the downstairs zone? I don't want to throw everything out of whack. But I'm thinking I would just put the upstairs on for an hour occasionally, and make sure that when I do, the downstairs zone is turned off. Would this make Speed 2 more realistic?

Also, I've got a 32 year old boiler, so dT is meant to be lower I think.

 

[Johntheo5]

Big time more realistic IMO as the pump head will then be ~ approaching 2.5M.

 

[JonathanM]

That sounds like a plan. I edited my post to add the bit about my boiler being really old and needing a smaller dT. Not sure if you saw that. Does that change anything?

 

[Johntheo5]

It will make it more difficult as the the smaller the dT the greater the circulation flow required, I wouldn't be too worried though about a dT of 12/15C and its effect on any type of boiler.

 

[JonathanM]

Great. Something fun to do tomorrow!